Modern electronic devices provide an increasing amount of functionality with a decreasing size. By continually integrating more and more capabilities within electronic devices, costs are reduced and reliability increased. Touch screens are frequently used in combination with conventional soft displays such as cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma displays and electroluminescent displays. The touch screens are manufactured as separate devices and mechanically mated to the viewing surfaces of the displays.
U.S. 2002/0175900 A1 by Armstrong, published Nov. 28, 2002, describes a touch system for use with an information display system including a frame defining an opening corresponding in size and shape to an information display area of a display. On each side is positioned an array of light emitting devices with a light-transmissive prism positioned along each array of light emitting devices such that light emitted from the light emitting devices is directed across the touch input area. The system also includes light detection devices positioned at each corner of the frame. In a preferred embodiment, the light emitting devices are organic light emitting diodes.
When such a touch screen is used with a flat panel display, the touch screen is simply placed over the flat panel display and the two are held together by a mechanical mounting means such as an enclosure. These prior-art arrangements combining touch screens and OLED displays suffer from a variety of drawbacks. The use of frames increases the parts count, weight, and cost of the device. The separation between the touch screen and display increases thickness. Redundant components found in the display and touch screen further increase cost and decrease performance as compared to more integrated solutions. Moreover, the need for separate cabling for the touch screen increases manufacturing costs.
Copending, commonly assigned U.S. Ser. No. 10/346,987 (filed Jan. 17, 2003) and Ser. No. 10/703,808 (filed Nov. 7, 2003) describe integrated OLED display and touch screen system comprising: a) a substrate; b) an OLED display area including an array of individually addressable OLEDs formed on the substrate; and c) a touch screen including at least one OLED light emitter formed on the substrate and at least one light sensor formed on the substrate across the display area from the light emitter, and optics located around the display area above the light emitter and the light sensor for directing light emitted from the light emitter across the display area to the light sensor. While advantageous, sensors employed in such an arrangement may not provide sufficient sensitivity and resolution to meet needs for some applications. Thus, there remains a desire for a further improved touch screen, flat-panel display system that minimizes device weight, removes redundant materials, decreases cost, eliminates special mechanical mounting designs, increases reliability, minimizes the degradation in image quality, and provides improved sensitivity and resolution.